Conventionally, there is proposed an active vibration noise control device for controlling an engine sound heard in a vehicle interior by a controlled sound output from a speaker so as to decrease the engine sound at a position of passenger's ear. For example, noticing that a vibration noise in a vehicle interior is generated in synchronization with a revolution of an output axis of an engine, there is proposed a technique for canceling the noise in the vehicle interior on the basis of the revolution of the output axis of the engine by using an adaptive notch filter so that the vehicle interior becomes silent, in Patent Reference-1.
By the way, in a narrow vehicle interior environment, there is a case that a deep dip of transfer characteristics from a speaker to a microphone occurs due to a sound wave interference and a reflection in a vehicle interior space. In such a frequency band that the deep dip occurs, an operation of the adaptive notch filter tends to become unstable, and a noise-canceling effect tends to decrease.
For example, in Patent Reference 1, there is proposed a technique for solving the above problem. In Patent Reference 1, there is proposed a technique for switching a speaker to be used in accordance with a noise frequency by using plural speakers. Concretely, the technique verifies transfer characteristics (in other words, amplitude characteristics. The same will apply hereinafter.) of paths related to the speakers, and selects a path of speaker in which an influence of the dip is small.
There are disclosed techniques related to the present invention in Patent References 2 and 3.